1. Field of the Invention
The present invention relates to the recovery of molybdenum catalyst from the epoxidation reaction product of olefins with organic hydroperoxides, and in particular, to recovery of the molybdenum catalyst with an ion exchange process.
2. Brief Description of the Related Art
The epoxidation reaction of propylene with tertiary butyl hydroperoxide (TBH) in the presence of a catalyst produces propylene oxide and tertiary butyl alcohol (TBA). The reaction mixture from the epoxidation reaction comprises unreacted propylene, propylene oxide, TBA, unreacted TBH, the catalyst and impurities. The generic name for this reaction is the epoxidation of olefins with organic hydroperoxides. The reaction mixture may be separated by distillation to produce a recycled propylene fraction, a propylene oxide fraction, a recycled TBA fraction, and a fraction containing substantially all the dissolved catalyst along with various impurities.
The preferred epoxidation catalyst is a glycol-molybdate complex which is prepared by heating a mixture of an ammonium-containing molybdenum compound such as ammonium dimolybdate (ADM) and a glycol such as ethylene glycol (EG) or propylene glycol (PG) in an autoclave reactor. Ammonia and water by-products are driven from the reaction mixture as vapors and condensed and collected in the overheads condenser system. The glycol-molybdate complex is then used in the epoxidation reaction system.
The prepared catalyst is converted into the “active form” during the epoxidation reaction. During the distillation process to purify the TBA formed in the epoxidation reaction, the active form of the glycol-molybdate complex accumulates in the bottom of the distillation towers. The glycol-molybdate catalyst and other high boiling compounds are removed as a tarry mixture from the process by a residue evaporation system. The tarry bottoms material can cause severe heat transfer surface fouling requiring frequent outages for tube bundle cleaning and/or replacement.
Conventional methods for the recovery of molybdenum from the high boiler residue are disclosed in U.S. Pat. Nos. 3,629,144; 3,931,044; 4,405,572; 4,845,251; 5,093,509; 5,101,052; 5,585,077; 5,731,446; and 5,776,848, the disclosures of which are incorporated herein by reference. It is known to recover molybdenum from high boiler residue by incineration. It is believed that hydrometallurgy may able to extract molybdenum from the incineration fly ash.
The limitations of the prior art are overcome by the present invention as described below.